Servlet实现文件上传

来源：互联网发布：linux route 修改编辑：程序博客网时间：2024/05/22 12:20

Servlet3.0开始新增了Part接口，专门用来处理文件上传。

package javax.servlet.http;import java.io.IOException;import java.io.InputStream;import java.util.Collection;public interface Part {    public InputStream getInputStream() throws IOException;    public String getContentType();//获得内容属性如image/png    public String getName();//获得input name属性值与request.getPart参数值一致    public String getSubmittedFileName();//获得上传文件名    public long getSize();    public void write(String fileName) throws IOException;//将上传内容写入文件    public void delete() throws IOException;    public String getHeader(String name);//根据标头名称返回标头信息    public Collection<String> getHeaders(String name);//根据标头名称返回标头信息集合    public Collection<String> getHeaderNames();//返回标头名称集合}

比较重要的几个方法：

/** * Obtain the content type passed by the browser. * * @return The content type passed by the browser or <code>null</code> if *         not defined. */public String getContentType();

获得文件类型信息，如image/jpeg;image/png。

/** * If this part represents an uploaded file, gets the file name submitted * in the upload. Returns {@code null} if no file name is available or if * this part is not a file upload. * * @return the submitted file name or {@code null}. * * @since Servlet 3.1 */public String getSubmittedFileName();

获得上传文件名称，如test.jpg

/** * A convenience method to write an uploaded part to disk. The client code * is not concerned with whether or not the part is stored in memory, or on * disk in a temporary location. They just want to write the uploaded part * to a file. * *  This method is not guaranteed to succeed if called more than once for *  the same part. This allows a particular implementation to use, for *  example, file renaming, where possible, rather than copying all of the *  underlying data, thus gaining a significant performance benefit. * * @param fileName  The location into which the uploaded part should be *                  stored. Relative locations are relative to {@link *                  javax.servlet.MultipartConfigElement#getLocation()} * * @throws IOException if an I/O occurs while attempting to write the part */public void write(String fileName) throws IOException;

上传文件。

/** * Obtain the size of this part. * * @return The size of the part if bytes */public long getSize();

获得上传文件大小（字节）。

Demo：

upload.html

<!DOCTYPE html><html><head>    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">    <title>upload</title></head><body>    <form action="upload.do" method="post" enctype="multipart/form-data">        上传图片：<input type="file" name="photo" value="" />        <br />        <input type="submit" value="上传" name="upload" />    </form></body></html>

uploadServlet.java

import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.Part;import java.io.IOException;import java.io.PrintWriter;import java.time.LocalDate;import java.time.LocalTime;import java.time.format.DateTimeFormatter;//import javax.servlet.annotation.MultipartConfig;//import javax.servlet.annotation.WebServlet;/** * Created by N3verL4nd on 2017/1/9. *///@MultipartConfig(location = "D:/JAVA/IdeaProjects/JavaProj/out/artifacts/jspRun_war_exploded/upload")//@WebServlet(name = "uploadServlet", urlPatterns = {"/upload.do"})public class uploadServlet extends HttpServlet {    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        request.setCharacterEncoding("UTF-8");        response.setContentType("text/html;charset=UTF-8");        PrintWriter out = response.getWriter();        Part part = request.getPart("photo");        //获得上传文件名称(实际过程中应该重命名自己想要的格式)        String filename = part.getSubmittedFileName();        //类型检查如：只要图片格式文件        if (part.getContentType().startsWith("image")) {            String finalFileName = getPreFileName() + filename.substring(filename.indexOf('.', 0), filename.length());            //写入文件            //part.write(finalFileName);            out.println("<h2>" + finalFileName + "  上传成功</h2>");        }        else {            out.println("<h2>上传失败</h2>");        }        //返回input标签name值(与request.getPart参数一致)        //out.println(part.getName());        /*//返回标头名称集合(如content-disposition;content-type)        for (String str : part.getHeaderNames()){            out.println(str + "<br />");        }*/        /*//根据标头名称返回标头详细信息(如form-data; name="photo"; filename="ing.png")        for (String str : part.getHeaders("content-disposition")){            out.println(str + "<br />");        }*/        /*        //返回内容类型        out.println(part.getContentType() + "<br />");        //返回标头信息        out.println(part.getHeader("content-disposition") + "<br />");        //返回上传文件大小        out.println(part.getSize() + " 字节");        //返回上传文件名        out.println(part.getSubmittedFileName());        */        //out.println(this.getServletContext().getRealPath("upload"));    }    //随机生成文件名    private String getPreFileName(){        StringBuilder stringBuilder = new StringBuilder();        LocalDate date = LocalDate.now();        //格式化日期字符串        stringBuilder.append(date.format(DateTimeFormatter.BASIC_ISO_DATE));        LocalTime time = LocalTime.now().withNano(0);        //格式化时间字符串        stringBuilder.append(time.format(DateTimeFormatter.ofPattern("HHmmss")));        return stringBuilder.toString();    }}

上传服务器文件名如：20170109214600.png

关于MultipartConfig：

@MultipartConfig

该注解主要是为了辅助 Servlet 3.0 中 HttpServletRequest 提供的对上传文件的支持。该注解标注在 Servlet 上面，以表示该 Servlet 希望处理的请求的 MIME 类型是 multipart/form-data。另外，它还提供了若干属性用于简化对上传文件的处理。具体如下：

表 5. @MultipartConfig 的常用属性

属性名类型是否可选描述fileSizeThresholdint是当数据量大于该值时，内容将被写入文件。locationString是存放生成的文件地址。maxFileSizelong是允许上传的文件最大值。默认值为 -1，表示没有限制。maxRequestSizelong是针对该 multipart/form-data 请求的最大数量，默认值为 -1，表示没有限制。

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